1. Field of the Invention
The present invention relates to a control apparatus for hybrid vehicles, and particularly relates to a control apparatus for hybrid vehicles for restricting the rotation speed of the engine when a failure of component related to the motor control is encountered.
2. Background Art
Electric cars are currently under development in order to reduce the discharge of exhaust gas into the atmosphere. However, the cruising range of electric cars driven only by a motor is limited by the capacity of the battery which stores the electric energy. If sufficient cruising range is desired, very large batteries are required, which seriously degrades the travelling performance of the car.
Hence, hybrid cars have become the subject of intensive development, because it is possible for hybrid cars to provide both a large cruising range, and good driving performance by using both an engine driven by the combustion of fossil fuel and a motor activated by a comparatively small battery.
Parallel-type hybrid vehicles, one type of hybrid vehicles, realize good driving performance, reduced emission of exhaust gas, and reduced fuel consumption by switching the driving modes from an engine drive mode to a motor drive mode according to the driving conditions.
That is, parallel-type hybrid cars travel using the engine only, when travelling using the engine is efficient, and the motor assists the engine or the motor drives the vehicle without the engine when the travelling conditions are not conductive to efficient use of the engine, such as when accelerating or when travelling slowly.
In addition, when braking the vehicle, the motor is operated as a generator for recovering the kinetic energy of the vehicle and energy loss can be prevented and the fuel consumption can be reduced.
In order to control the above described motor, it is necessary to provide a variety of components such as a control apparatus for controlling the motor, a signal line for transmitting signals from the control apparatus, sensors for detecting voltages or electric currents between the motor and the battery and for transmitting these values to the control apparatus. Furthermore, the above described control apparatus comprises a CPU (Central Processing Unit) and a memory, and the control function is realized by executing a program for the functions of the control apparatus. These components, apparatuses, and software related to the motor are called a motor system, and are indispensable for driving the motor.
When a failure is encountered in the motor system while driving hybrid cars, and when the motor cannot be controlled normally, it is necessary to stop the motor immediately and to switch to a driving mode using only the engine. In this case, the peripheral components around the motor must be protected from the voltage generated by regeneration by the motor.